Transformation optics

About: Transformation optics is a research topic. Over the lifetime, 2687 publications have been published within this topic receiving 102378 citations.

Infrared magnetic response in a random silicon carbide micropowder

Abstract: We generalize the theoretical model of magnetic metamaterials made of dielectric particles to treat random particle sizes, shapes, and orientations. We demonstrate that the magnetic-dipole response of these randomly shaped subwavelength particles can be approximated with Mie theory as though they were spheres, while a quasistatic ellipsoidal approximation is used for the electric-dipole response. We verify our model with experimental measurement of a bulk magnetic response in a micropowder of milled SiC particles. Using such a crude powder could lead to immensely simplified negative permeability inclusions for negative index metamaterials.

Experimentally demonstrated a unidirectional electromagnetic cloak designed by topology optimization

Abstract: Electromagnetic invisible devices usually designed by transformation optics are rather complicated in material parameters and not suitable for general applications. Recently, a topology optimized cloak based on level-set method was proposed to realize nearly perfect cloaking [Fujii et al., Appl. Phys. Lett. 102, 251106 (2013)]. In this work, we experimentally implemented this idea and fabricated a unidirectional cloak with a relative large invisible region made of single dielectric material. Good cloaking performance was verified through measurement which consists very well with numerical simulation. The advantages and disadvantages of this optimization method are also discussed.

On the signs of the imaginary parts of the effective permittivity and permeability in metamaterials

Abstract: The signs of the imaginary parts of the permittivity and permeability in metamaterials such as split ring resonators and strip wires are investigated. It is shown that the Lorentzian model often used to describe the effective parameters (i.e., the permittivity and permeability) of these metamaterials does not physically allow their imaginary parts to be negative. Moreover, a popular technique used to retrieve the effective parameters of a structure from its S-parameters is also investigated. By comparing the effective parameters for an array of dielectric spheres obtained both from S-parameter simulations and analytical calculations, it is shown that an often observed negative imaginary permittivity obtained from the S-parameters is a result of numerical error in the simulations. This is shown both for the finite element method and finite-difference time-domain simulations.

Optical Surface Transformation: Changing the optical surface by homogeneous optic-null medium at will.

Abstract: A new theory on designing electromagnetic/optical devices is proposed, namely, an optical surface transformation (OST). One arbitrary surface can establish the corresponding relationship with another surface entirely optically with an optic-null medium (ONM), (i.e. the electromagnetic wave propagates from one surface to its equivalent surface without any phase delay). Many novel optical devices can be designed by an OST with the help of an ONM. Compared with traditional devices designed by Transformation Optics, our optical surface-reshaping devices have two main advantages. Firstly, the design process is very simple (i.e. we do not need to consider any mathematics on how to make a coordinate transformation, and what we need to do is simply to design the shapes of the input and the output surfaces of the devices). Secondly, we only need one homogeneous anisotropic medium to realize all devices designed by this method. Our method will explore a new way to design novel optical devices without considering any coordinate transformations.

Making Waves Round a Structured Cloak: Lattices, Negative Refraction and Fringes

Abstract: Using the framework of transformation optics, this paper presents a detailed analysis of a non-singular square cloak for acoustic, out-of-plane shear elastic, and electromagnetic waves. The generating map is examined in detail and linked to the material properties of the cloak. Analysis of wave propagation through the cloak is presented and accompanied by numerical illustrations. The efficacy of the regularised cloak is demonstrated and an objective numerical measure of the quality of the cloaking effect is provided. It is demonstrated that the cloaking effect persists over a wide range of frequencies. As a demonstration of the effectiveness of the regularised cloak, a Young's double slit experiment is presented. The stability of the interference pattern is examined when a cloaked and uncloaked obstacle are successively placed in front of one of the apertures. This novel link with a well-known quantum mechanical experiment provides an additional method through which the quality of cloaks may be examined. In the second half of the paper, it is shown that an approximate cloak may be constructed using a discrete lattice structure. The geometry and material properties of the lattice are derived from the continuum cloak. The efficiency of the approximate lattice cloak is analysed and a series of illustrative simulations presented. It is demonstrated that effective cloaking may be obtained by using a relatively simple lattice structure, particularly in the low frequency regime.